There are many carts, devices and or carriages that rely upon rails, tracks, ropes, or cables for propulsion or guidance. Commuter trains, for example, ride on tracks or railways. The train engine may pull a sequential link of carriages on the tracks or railway. One of the disadvantages of the track or railway system is that the individual carriages are not easily or “at will” interchangeable in their order on a track. The difficulty in interchanging the carriages may be a lack of individual engines for each carriage or that the carriages are all sequentially laid out, in line, and linked on a single bi-directional track.
The interchangeability problem may also be seen in aerial tramways and telpher systems. The individual cable cars or carriages may be bound to the bi-directional cable or the track from which it is suspended. The limited bi-directionality may limit the cable cars from interchanging their position on the cable or track and may limit them from moving perpendicular to the track. Even if each car on the track is self-propelled or individually motorized, individual cars may still be limited in their movement by the cable car in front or in back of the individual cars.